Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for acquiring a two-dimensional image from information on a tomographic image acquired by optical interference.
Description of the Related Art
An image acquiring apparatus that performs optical coherence tomography (OCT) utilizing an interference phenomenon of multi-wavelength light (hereinafter referred to as “OCT apparatus”) has been known. The OCT apparatus is used for obtaining, for example, information on organs with an endoscope and information on a retina with an ophthalmologic apparatus, and the application thereof to human bodies is expanding. In particular, the OCT apparatus applied to an eye is becoming an indispensable apparatus as ophthalmologic instrument for a specialist of retina in the outpatient field.
The OCT apparatus is capable of irradiating a sample with measurement light having low coherence and measuring backscattered light from the sample through use of an interference system, to thereby acquire an image. When the OCT apparatus is applied to an eye, the OCT apparatus can photograph a tomographic image of an eye to be inspected with high resolution by scanning the eye to be inspected with the measurement light.
Further, there has been known a technology of forming a two-dimensional image of a fundus viewed from the front in a pseudo manner (hereinafter referred to as “two-dimensional image”) from a plurality of tomographic images. In a method of forming a two-dimensional image, a pixel value is selected based on an order of a magnitude of pixel values from pixel value rows in a depth direction acquired by one A-scan. Then, the selected pixel value is obtained with respect to all the A-scans, to thereby form a two-dimensional image similar to a planar image of a retina (Projection image) only with tomographic images (Japanese Patent Application Laid-Open No. 2014-45869).
Further, in Japanese Patent Application Laid-Open No. 2014-45869, there is also described a method of forming a two-dimensional image regarding a predetermined layer of a retina in the case of selecting the predetermined layer. In this method, a pixel value is selected based on an order of a magnitude of pixel values from pixel value rows within the layer, to thereby form a two-dimensional image.
All the pixel value rows in a depth direction of a retina and pixel value rows within a range including a predetermined layer in the depth direction are significantly different from each other in ratio of an object to be measured in the pixel value rows. Therefore, when a pixel value is selected based on the same criteria in the case of selecting one pixel value from all the pixel value rows in the depth direction and in the case of selecting one pixel value from the pixel value rows within the predetermined range, a satisfactory two-dimensional image may not be acquired.
Further, for example, when an attempt is made to acquire a two-dimensional image of a layer having a lesion, a pixel value corresponding to a tissue influenced by the lesion may be significantly different from that of a surrounding portion. When the same criteria are used in this case, there is a risk in that a pixel value corresponding to the lesion may be deleted.